This invention relates to a keyboard switch and, more particularly, to a keyboard switch having membrane contacts.
A wide variety of switches have been proposed to make keyboards thinner. Japanese Utility Patent Publication No. 12332 of 1980 discloses examples of such switches. As shown in FIG. 4(a) and (b) of this reference, two fixed contacts of printed wiring sit on an insulating baseplate separated by an insulating spacer from a conductive, elastic sheet whose pipe-shaped portion is within a housing and directly beneath a key top. When the key top is depressed, the pipe-shaped portion is flexed to short out the two fixed contacts, thus closing an electrical circuit.
Japanese Laid-open Utility Model Publication No. 101915 of 1986 also discloses a keyboard switch, which, as shown in FIG. 5., used two fixed contacts on an insulating baseplate beneath a box-shaped housing. An elastic contact member with two moving contacts is mounted at the base of a key stem beneath a key top. Pressing down the key top connects the two fixed contacts and the moving contacts, thereby closing a circuit.
In the key shown in FIG. 5, depressing the key deforms the elastic contact member, collapsing a thin-wall portion thereof to produce a click feel. If the key top is further depressed, the moving contacts touch the fixed contacts 13 to energize a circuit.
This prior art has drawbacks. Regarding the keyboard switch shown in FIG. 4, the continued operation of a keyboard without a click feel causes fatigue. Also, a keyboard with this type of key is bulky, because the insulating spacer must be thick enough to keep the two fixed contacts from contacting the pipe-shaped portion under normal conditions when the key top is not pressed down. Further, since the pipe-shaped portion is formed integrally with the elastic conductive sheet, the mechanism is not flexible enough to be used in some keyboards. Regarding the keyboard switch shown in FIG. 5, although a switch having such a click feel may operate satisfactorily without causing fatigue, the height of elastic contact member is too great to be suitable for a thin keyboard.